This invention relates to bar code scanners and, in particular, to bar code scanners capable of automatically scanning bar code data without a manually activated mechanical trigger to initiate a scan of bar code data.
Known hand held bar code scanners include a scanning head ("scanner") connected to a decoder box with the scanner including a manual mechanical trigger for, when depressed, initiating a scanning interval. Typically, an operator of a bar code scanner sights a bar code to be read and after aiming the scanner at the bar code depresses a manually activated mechanical trigger initiating a scanning cycle. In response to the manual actuation of the mechanical trigger the following events occur. The scanner emits a light beam which illuminates the bar code and light impinging on the bar Code is reflected back to the scanner. Concurrently, the scanner produces a "trigger pulse" which is applied to the decoder box to activate the decoder box and prepare it to receive bar code data signals. When the decoder box is ready to receive bar code data it produces an "enabling signal" [e.g., a power enable (PE) pulse] which it supplies to the scanner to indicate that the decoder box is ready to receive bar code data from the scanner. In response to the "enabling signal" a bar code scanner typically generates a train of start of scan (SOS) pulses having an "integrate" period followed by a "read" period. The SOS pulses are then applied to the electronic circuitry contained within the scanner. During the "read" period of each SOS pulse, bar code data reflected from the bar code is fed to the decoder box where it is analyzed. When the decoder box recognizes that a "good" (i e., "valid") set of bar code data has been sensed it generates an end of scan signal terminating the scanning cycle initiated by the actuation of the manual trigger. Thus, after a valid set of bar code data is decoded the SOS pulses are terminated and the scanner is reset and placed in a condition such that the next manual trigger starts a new scanning cycle. Thus, by means of the manual trigger multiple reads are avoided.
In many applications it is desired to have a hand held scanner which can "automatically" scan bar codes without the manual actuation of a mechanical trigger. The "automatic" or non-manually triggered scanning of bar codes eliminates the need for a mechanical trigger. Also, automatic or electronic scanning eliminates the need to repeatedly manually depress a trigger which some users find objectionable. Eliminating the need for a manually operated mechanical trigger switch avoids mechanical wear and increases the reliability of the system. Furthermore, automatic or electronic scanning may speed up the scanning process.
To make use of presently available equipment, it is also desirable that the "automatic" scanner be capable of being directly coupled to existing decoder boxes with the decoder boxes being operated as if a manually triggered scanner was connected to the decoder box. Thus the automatic scanner must be such that it can be interchanged for a manually triggered scanner without requiring the existing decoder boxes to be changed in any way. This poses significant problems as discussed below.
For an "automatic" bar code scanner to be able to recognize the presence of a bar code and to read the bar code data without the use of a manual trigger, the "automatic" scanner must be continuously enabled. This gives rise to a basic problem which exists whenever it is desired to automatically scan bar code data without the use of a manual trigger. Since an "automatic" hand held scanner is continuously enabled, such a scanner although it has just read bar code data and has validated the data, will then tend to reread the bar code it has just read. To prevent this obviously unacceptable condition the scanner must be disabled after it reads and validates a "good" set of bar code data. However, if the scanner is disabled it is evident that the scanner must then be re-enabled in order to "automatically" read another bar code. Accordingly, one problem to be solved is how to disable the scanner so it does not re-read the same bar code data and how to re-enable the scanner so it can automatically read a new bar code (other than the one just read) without manually activating a mechanical switch. Another problem is to have the "automatic" scanner interface with a existing decoder box such that it is transparent to the decoder box whether an "automatic" scanner or a manually triggered scanner is connected to it. This requires that the "automatic" scanner be able to generate a "trigger" pulse when ready to read data and supply the trigger pulse to the decoder box and for the scanner to be responsive to an "enabling signal" to initiate the supply of bar code data to a decoder box for analysis.